Cure system, adhesive system, electronic device

ABSTRACT

A cure system including a compatiblized and passivated refectory solid dispersed within a low temperature liquid curing agent is provided. An adhesive system including the cure system is provided, and an associated method. A device including the cured adhesive system is provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit and priority to U.S. Provisional patentapplication Ser. No. 60/668,651, filed Apr. 5, 2005. The entire contentsof which are hereby incorporated by reference.

BACKGROUND

The invention includes embodiments that relate to a cure system and anadhesive system. The invention includes embodiments that relate to anelectronic device made using the cure system and adhesive system.

Semiconductor chips may be mounted to a substrate in an electronicdevice. The mounting may not be perfect and air-filled gaps may resultbetween a surface of the chip and a surface of the mounting substrate.Because the air gaps may be undesirable, an underfill resin may be usedto fill in the gaps. Underfill material may be used to improvereliability of the device. Further, the use of an underfill material mayimprove a fatigue life of solder bumps in an assembly.

To address shortcomings associated with traditional capillary underfillresins, a No-Flow Underfill (NFU) material was developed. No-FlowUnderfill may include a curable resin, such as an epoxy resin, and maybe unfilled, or filled with nano-size filler. The resin filler may befunctionalized colloidal silica. The higher the filler content in theresin, the closer may be a match of the coefficient of thermal expansion(CTE) of the cured resin relative to a semiconductor chip.Unfortunately, for reasons of processability and the like, fillerloadings of more than about 50 weight percent in the uncured resin maybe problematic. To exacerbate the situation, after the addition of acuring agent, the final filler loading may be below 30 weight percent ofthe total composition. A typical CTE of a cured no-flow underfill epoxyresin with filler loading below 30 weight percent may be above 50 ppm/°C.

It may be desirable to have an underfill material having one or more ofa coefficient of thermal expansion of less than 50 ppm/° C., a fillerloading of greater than 30 weight percent, an acceptable level ofprocessability, transparency, or a desirably high glass transitiontemperature (Tg). It may be desirable to have a process for makingand/or using an underfill material system having improved or differentproperties than are currently available. It may be desirable to have anapparatus or article employing a no-flow underfill material systemhaving improved or different properties than are currently available.

BRIEF DESCRIPTION

In one embodiment in accordance with the invention, a hardener or curingagent system may include a compatiblized and passivated refectory soliddispersed within a hardener or a curing agent, which are liquid at lowtemperature.

In another embodiment, an adhesive system may include the cure systemmixed with a curable epoxy resin.

According to another embodiment, a method may include dispersing acompatiblized and passivated refectory solid into a mixture or solutionof a liquid curing agent and a low boiling solvent. The solvent may befree of hydroxyl-groups. The solvent may be removed from the mixture orsolution to form a solvent-free liquid dispersion of curing agent andthe compatiblized and passivated refectory solid. One embodimentprovides an electronic device produced by the method.

An embodiment of the invention may include a solvent-free adhesivesystem for use in an electronic device. The adhesive system may includea curable epoxy resin and a cure system. The epoxy resin may include afirst portion of compatiblized and passivated refectory solid. The curesystem may include a low temperature liquid curing agent and a secondportion of compatiblized and passivated refectory solid, and may curethe resin. The compatiblized and passivated refectory solid may bepresent in an amount greater than about 30 percent by weight relative tothe total weight of the adhesive system.

In one embodiment, an electronic device may include a substrate, a chipsecured to the substrate, and a cured adhesive system according toembodiments of the invention disposed between the chip and thesubstrate.

DETAILED DESCRIPTION

The invention includes embodiments that relate to a cure systemcomprising a compatiblized and passivated refectory solid and a hardeneror a curing agent (collectively “curing agent”). The curing agent may beliquid or fluid at a low temperature. The invention includes embodimentsthat relate to methods of making and/or using the cure system. In oneembodiment, an adhesive system includes the cure system in combinationwith a curable resin. Other embodiments relate to electronic devicesmade using the adhesive system.

As used herein, cured refers to a curable composition having reactivegroups in which more than half of the reactive groups have reacted orcross linked; curing agent refers to a material that may interact with acurable resin to crosslink monomers in a resin system, such as an epoxyresin. Approximating language, as used herein throughout thespecification and claims, may be applied to modify any quantitativerepresentation that could permissibly vary without resulting in a changein the basic function to which it is related. Accordingly, a valuemodified by a term or terms, such as “about”, may not to be limited tothe precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value.

Hydroxyl-free, hydroxyl-group free, solvent-free, no-flow, and the likeinclude a complete absence of the indicated material or property, andfurther include a substantial absence of the indicated material. Thatis, the “no-” and “-free” modifiers, and the like, are not used in astrict or absolute sense and may contain insignificant, trace, residualor minimal amounts of the indicated material or property unless contextor language indicates otherwise. Derivatives may include conjugate acidsor salts. Stability, as used herein in the specification and claims,refers to the lack of reaction, or the lack thereof, of activetermination sites on the surface of the refractory solid and the curingagent over a period of time, e.g., one week, two weeks, and the like.The term “functionalized” may refer to a material in which initiallyfunctional groups have been manipulated or affected in some manner, suchas reacted with a compatibilizing material or a passivating material.

In one embodiment, a room temperature liquid cure system may include acompatiblized and passivated refectory solid and a liquid curing agent.The cure system may be combined with a curable resin to initiate cure ofthe resin, that is, to crosslink reactive monomers contained in theresin. Particularly, the compatiblized and passivated refectory solidmay be homogeneously dispersed into a low temperature liquid curingagent as filler to form the cure system. In one embodiment, the curesystem may be combined with a curable resin to form an adhesive system.The adhesive system may cure quickly after combining, may have a potlife that extends for hours or days, or may have an indefinite pot lifeor desirable shelf life until a further triggering event occurs, such asthe application of energy to the adhesive system. Such energy mayinclude thermal energy, e-beam energy, UV light, and the like.

Suitable compatiblized and passivated refectory solid may include aplurality of particles of one or more metal, metalloid, ceramic, ororganic material. Refractory may include materials with a high meltingtemperature, such as melting temperatures in a range of greater thanabout 1000 degrees Celsius. In one embodiment, the solid may includealuminum, antimony, arsenic, beryllium, boron, carbon, chromium, copper,gallium, gold, germanium, indium, iron, hafnium, magnesium, manganese,molybdenum, phosphorous, silicon, silver, titanium, tungsten, orzirconium, or the like, or an alloy of two or more thereof. In oneembodiment, the solid may include one or more of arsenic, aluminum,boron, gallium, germanium, silicon, titanium, or an oxide or nitridethereof, such as alumina, silica, titania, boron nitride, and the like.For ease of reference, silica may be used as a non-limiting example of asuitable solide. Silica may include colloidal silica (CS), fused silica,or fumed silica, and the like.

Prior to compatibilizing and passivating, a suitable solid oxide mayhave an active surface termination site that comprises a silanol orhydroxyl group. A suitable solid nitride may have the active surfacetermination site include an amide or an imide. Subesquent tocompatibilizing and passivating, the density of active termination sitesmay be controlled to be in a predetermined range. For example, withcolloidal nano-particle silica the active termination site density maybe about 5 active sites per square nanometer (OH/nm²) or less, about4.75 OH/nm² or less, or in a range of from about 50 H/nm² to about 10H/nm², from about 50 H/nm² to about 3 OH/nm², or from about 4.5 OH/nm²to about 4.0 OH/nm². Because the active termination site density maycorrespond to shelf life or stability, a suitable stability ratio (theratio of viscosity (two weeks/initial)), may be less than about 5, lessthan about 4, less than about 3 less than about 2, or about 1.

As noted hereinabove, compatibilizing and passivating or capping activetermination sites may be accomplished by, for example, a sequentialtreatment. A first portion of active surface termination sites may bereacted with a compatiblizing composition. A suitable compatiblizingcomposition may include those disclosed hereinabove, such as analkoxysilane having an organic moiety that may be one or more ofacrylate, alkyl, phenyl, cyclohexyloxy, or glycidyl. Of the remainingactive termination sites, a second portion may be reacted with apassivating composition, such as a silazane or other capping agent asdisclosed herein.

A suitable water dispersion of colloidal silica for use as a precursorto compatiblized and passivated colloidal silica may be commerciallyobtained from, for example, Nissan Chemical America Corporation(Houston, Tex.) under the tradename SNOWTEX, or NALCO 1034A, which isavailable from Nalco Chemical Company (Napier, Ill.). SNOWTEX 40 has anaverage particle size in a range of from about 10 nanometers to about 30nanometers.

The refectory solid initially may be hydrophilic or somewhatincompatible with an organic or non-polar phase due to the presence ofactive termination sites on the particle surface. For example, colloidalsilica may be hydrophilic due to the presence of silanol groups at thesurface. The hydrophilicity may make dispersion in an organic phaseproblematic or impracticable. Compatiblizing the solid surface maycreate an organophilic coating on the surface of the solid particles tomake the particles dispersible in, or compatible with, an organic phaseor a non-polar liquid. Compatiblizing may be accomplished with, forexample, a trialkoxy organosilanes (e.g., phenyl trimethoxy silane,glycidoxy propyl trimethoxy silane, and the like). To reduce further thecontent or density of active termination sites on the surface, thecompatiblized refectory solid may be post treated or reacted with acapping agent or a passivating agent. The reaction with the cappingagent may form particles with a relatively low content of availablehydroxyl or silanol groups. As disclosed above, such functional groupsmay be referred to as active termination sites.

A compatibilized refectory solid may be further treated or capped withone or more capping agent for passivation. Suitable capping agents mayinclude one or more of a triorganosilane, an organodisilazane,organoalkoxysilane, or an organohalosilane such as organochlorosilane.In one embodiment, the capping agent may include one or more ofhexamethyl disilazane (HMDZ), tetramethyl disilazane, divinyltetramethyl disilazane, diphenyl tetramethyl disilazane, N-(trimethylsilyl) diethylamine, 1-(trimethyl silyl) imidazole, trimethylchlorosilane, pentamethyl chloro disiloxane, trimethylmethoxysilane andpentamethyl disiloxane, and the like.

An acid, a base, or a condensation catalyst may be used to promotecondensation of, for example, silanol groups on a silica particlesurface and an alkoxy silane group to compatiblize the silica particle.Suitable condensation catalysts may include organo-titanate andorgano-tin compounds such as tetrabutyl titanate, titanium isopropoxybis (acetyl acetonate), dibutyltin dilaurate, and the like, orcombinations of two or more thereof.

The compatiblized and passivated (e.g., capped) particles may have arelatively reduced number and/or density of active termination sites onthe particle surface. The reduced number or reduced density may providea stable dispersion of particles in a curing agent, a curable resin, ora mixture of both curing agent and curable resin. Further, reduceddensity of active termination sites (e.g., hydroxyl content oncompatiblized and passivated silica) may reduce or eliminate reactionswith an anhydride, which may otherwise react with, for example,available hydroxyl groups. Such anhydride/hydroxyl reactions may form afree acid. Thus, reducing or eliminating active termination sites, suchas by passivation, may reduce or eliminate free acid formation and mayincrease stability.

The amount of refectory solid present in a cure system may be expressedas a weight percent of the total weight. The refectory solid may bepresent in a cure system in an amount greater than about 0.5 weightpercent, or in a range of from about 0.5 weight percent to about 80weight percent. In one embodiment, the refectory solid content may bepresent in a cure system in an amount in a range of from about 1 weightpercent to about 5 weight percent, from about 5 weight percent to about10 weight percent, from about 10 weight percent to about 20 weightpercent, from about 20 weight percent to about 30 weight percent, fromabout 30 weight percent to about 40 weight percent, from about 40 weightpercent to about 50 weight percent, from about 50 weight percent toabout 60 weight percent, or greater than 60 weight percent.

Suitable refractory solids may have a surface area greater than about 20square meters per gram, greater than about 60 square meters per gram, orgreater than about 150 square meters per gram. The solid may include aplurality of nano-particles having an average diameter in a range offrom about 1 nanometer to about 100 nanometers. In one embodiment, therefractory solids may have an average particle size of less than about 1micrometer to about 500 nanometers, from about 500 nanometers to about250 nanometers, from about 250 nanometers to about 100 nanometers, fromabout 100 nanometers to about 50 nanometers, from about 50 nanometers toabout 25 nanometers, from about 25 nanometers to about 10 nanometers,from about 10 nanometers to about 5 nanometer, or less than about 5nanometer.

Suitable particles may have one or more of a spherical, amorphous orgeometric morphology. In one embodiment, the particles may be amorphous.Suitable particles may be porous, may be non-porous, or may include someporous and some non-porous particles. The pores may be uniform in shapeor size, or may be shaped and/or sized differently from each other.

A suitable low temperature liquid curing agent may include an anhydride,such as carboxylic acid anhydride, with a relatively low melt point(below about 100 degrees Celsius) or that may be liquid at about roomtemperature. Low temperature may include temperatures in a range of lessthan about 100 degrees Celsius, and particularly may includetemperatures in a range of less than about 50 degrees Celsius. In oneembodiment, the curing agent is a flowable liquid in a temperature rangeof from about 25 degrees Celsius to about 35 degrees Celsius.

Liquid refers to a property of being fluid or able to flow orthermoplastically deform. A measure of fluidity may be expressed asviscosity, which is the degree to which a fluid may resist flow under anapplied force, as measured by the tangential friction force per unitarea divided by the velocity gradient under conditions of streamlineflow. In one embodiment, the cure system at low temperature may have aBrookfield viscosity of less than about 1000 Poise, in a range of from1000 Poise about to about 100 Poise, from about 100 Poise to about 1000centipoise, from about 1000 centipoise, or less than about 1000centipoise. Viscosity may be measured according to ASTM D-2393-67, whichis incorporated herein by reference. The viscosity may differ fromembodiment to embodiment, for example, in response to changes in fillerloading or type, temperature, and selection of curing agent.

Suitable liquid or low melting temperature anhydrides may include one ormore aromatic anhydride, aliphatic anhydride, or cycloaliphaticanhydride. The curing agent may include one or more carboxylic acidanhydrides, which may be selected from aromatic carboxylic acidanhydride, aliphatic carboxylic acid anhydride, or cycloaliphaticcarboxylic acid anhydride. Carboxylic anhydrides may be prepared byreacting a carboxylic acid with an acyl halide, or by dehydrating acarboxylic acid, that is, eliminate water between two carboxylic acidmolecules to form the anhydride. Alternatively, carboxylic acidanhydrides may be obtained commercially from common chemical suppliers.

Aromatic anhydrides may include one or more of benzoic anhydride;phthalic anhydride; 4-nitrophthalic anhydride; naphthalenetetracarboxylic acid dianhydride; naphthalic anhydride; tetrahydrophthalic anhydride; derivatives thereof; and the like. In oneembodiment, a curing agent may include one or more aromatic carboxylicacid anhydrides. Cycloaliphatic anhydrides may include one or more ofcyclohexane dicarboxylic anhydride, hexahydro phthalic anhydride,methyl-hexahydro phthalic anhydride (MHHPA), derivatives thereof, andthe like. In one embodiment, a curing agent may include5,5′-(1,1,3,3,5,-hexamethyl-1,5-trisiloxane diyl) bis[hexahydro-4,7-methanoisobenzofuran-1,3-dione] (TriSNBA), which iscommercially available from GE Silicones (Waterford, N.Y.).

Structures of some other suitable anhydrides are shown below.

In one embodiment, a curing agent may include one or more of butanoicanhydride; dodecenyl succinic anhydride; 2,2-dimethyl glutaricanhydride; ethanoic anhydride; glutaric anhydride; hexafluoro glutaricacid anhydride; itaconic anhydride; tetrapropenylsuccinic anhydride;maleic anhydride; 2-methyl glutaric anhydride; 2-methyl propionicanhydride 1,2-cyclohexane dicarboxylic anhydride; octadecyl succinicanhydride; 2-or n-octenyl succinic anhydride; 2-phenylglutaricanhydride; propionic acid anhydride; 3,3-tetramethylene glutaricanhydride; derivatives thereof; and the like.

The cure system may be blended, dispersed and/or mixed into a curableresin to form an adhesive system. In one embodiment, the resin may havea filler pre-dispersed therein. That is, prior to mixing both the curesystem and the resin system each have a high content of refractorysolids dispersed therein.

Suitable resins may include one or more aliphatic epoxy resins,cycloaliphatic epoxy resins, or aromatic epoxy resins. Suitablealiphatic epoxy resins may include one or more of butadiene dioxide,dimethyl pentane dioxide, diglycidyl ether, 1,4-butanediol diglycidylether, diethylene glycol diglycidyl ether, and dipentene dioxide, andthe like. Suitable aliphatic epoxy monomers may include one or more ofbutadiene dioxide, dimethylpentane dioxide, diglycidyl ether, 1,4-butanediol diglycidyl ether, diethylene glycol diglycidyl ether, ordipentene dioxide, and the like. In one embodiment, the aliphaticdioxirane monomer may include CYRACURE UVR 6105, which is commerciallyavailable from Dow Chemical (Midland, Mich.).

Suitable cycloaliphatic epoxy resins may include one or more of3-cyclohexenyl methyl-3-cyclohexenyl carboxylate diepoxide;2-(3,4-epoxy) cyclohexyl-5,5-(3,4-epoxy) cyclohexane-m-dioxane;3,4-epoxy cyclohexyl alkyl-3,4-epoxy cyclohexane carboxylate;3,4-epoxy-6-methyl cyclohexyl methyl-3,4-epoxy-6-methyl cyclo hexanecarboxylate; vinyl cyclohexane dioxide; bis (3,4-epoxy cyclohexylmethyl) adipate; bis (3,4-epoxy-6-methyl cyclohexyl methyl) adipate; bis(2,3-epoxy cyclopentyl) ether; 2,2-bis (4-(2,3-epoxy propoxy)cyclohexyl) propane; 2,6-bis (2,3-epoxy propoxy cyclohexyl-p-dioxane);2,6-bis (2,3-epoxy propoxy) norbornene; diglycidyl ether of linoleicacid dimer; limonene dioxide; 2,2-bis (3,4-epoxy cyclohexyl) propane;dicyclopentadiene dioxide; 1,2-epoxy-6-(2,3-epoxy propoxy)hexahydro-4,7-methanoindane; p-(2,3-epoxy) cyclopentylphenyl-2,3-epoxypropyl ether; 1-(2,3-epoxy propoxy) phenyl-5,6-epoxyhexahydro-4,7-methanoindane; (2,3-epoxy) cyclopentyl phenyl-2,3-epoxypropyl ether); 1,2-bis (5-(1,2-epoxy)-4,7-hexahydro methano indanoxyl)ethane; cyclopentenyl phenyl glycidyl ether; cyclohexane diol diglycidylether; diglycidyl hexahydrophthalate; and 3-cyclohexenylmethyl-3-cyclohexenyl carboxylate diepoxide; and the like. In oneembodiment, a cycloaliphatic epoxy monomer may include one or more3-cyclohexenyl methyl-3-cyclohexenyl carboxylate diepoxide, 3-(1,2-epoxyethyl)-7-oxabicycloheptane; hexanedioic acid, bis (7-oxabicyclo heptylmethyl) ester;2-(7-oxabicyclohept-3-yl)-spiro-(1,3-dioxa-5,3′-(7)-oxabicyclo heptane;and methyl 3,4-epoxy cyclohexane carboxylate, and the like.

Suitable aromatic epoxy resins may include one or more of bisphenol-Aepoxy resins, bisphenol-F epoxy resins, phenol novolac epoxy resins,cresol-novolac epoxy resins, biphenol epoxy resins, biphenyl epoxyresins, 4,4′-biphenyl epoxy resins, polyfunctional epoxy resins,divinylbenzene dioxide, resorcinol diglyciyl ether, and 2-glycidylphenyl glycidyl ether. Other suitable resins may include silicone-epoxyresins and siloxane epoxy resins. Bisphenol-F resins may be commericallyavailable from Resolution Performance Products (Pueblo, Colo.).

Optional additives may be incorporated into the resin portion of thesystem, the curing agent portion of the system, or both. Suitableadditives may include one or more catalyst, accelerator, flexibilizer,carbinol, organic diluent, fire retardant, pigment, thermally conductivefiller, electrically conductive filler, thermally insulative filler,electrically insulative filler, and the like.

A suitable catalyst or accelerator may initiate a crosslinking process,accelerate cure rate, or decrease cure time or temperature of anadhesive system. A catalyst or accelerator may be present in an amountless than about 10 parts per million (ppm), in a range of from about 10ppm to about 100 ppm, from about 100 ppm to about 0.1 weight percent,from about 0.1 weight percent to about 1 weight percent, or greater thanabout 1 weight percent of the total formulation weight.

A suitable catalyst or an accelerator may include, but is not limitedto, an onium catalyst or a free-radical generating compound. Suitableonium catalysts may include bisaryliodonium salts (e.g. bis (dodecylphenyl) iodonium hexafluoro antimonate, (octyl oxyphenyl phenyl)iodonium hexafluoro antimonate, bisaryl iodonium tetrakis (pentafluorophenyl) borate), triaryl sulphonium salts, and combinations of twoor more thereof. Suitable free-radical generating compounds may includeone or more aromatic pinacols, benzoinalkyl ethers, organic peroxides,and the like. The presence of a free radical generating compound mayenable decomposition of an onium salt at a relatively lower temperature.

In one embodiment, a catalyst or an accelerator may be added to anepoxy-based adhesive system. Useful catalysts or accelerators mayinclude one or more amine; alkyl-substituted imidazole; imidazoliumsalt; phosphine; metal salt, such as aluminum acetyl acetonate(Al(AcAc)₃); salt of nitrogen-containing compound; and the like. Thenitrogen-containing compound may include, for example, one or more aminecompounds, di-aza compounds, tri-aza compounds, polyamine compounds andthe like. A salt of a nitrogen-containing compound may include, forexample 1,8-diazabicyclo (5,4,0)-7-undecane. The salt of thenitrogen-containing compounds may be obtained commercially, for example,as POLYCAT SA-1 or POLYCAT SA-102. POLYCAT SA-1 is a delayed-action,heat-activated catalyst based on the cyclic amine, 1,8 diaza-bicyclo(5,4,0) undec-ene-7. POLYCAT SA-1 contains DBU catalyst and an organicacid “blocker”. POLYCAT is a trademark of Air Products and Chemicals,Inc (Allentown, Pa.). Other suitable catalysts may include triphenylphosphine (TPP), N-methylimidazole (NMI), and/or dibutyl tin dilaurate(DiButSn).

Additives, such as flexibilizers, may include one or more organiccompounds having a hydroxyl-containing moiety. Suitable flexibilizersmay include one or more of polyol or bisphenol. The polyol may bestraight chain, branched, cycloaliphatic, or aromatic and may containfrom about 2 to about 100 carbon atoms. Examples of such polyfunctionalalcohols may include one or more of ethylene glycol; propylene glycol;2,2-dimethyl-1,3-propane diol; 2-ethyl, 2-methyl, 1,3-propane diol;1,3-pentane diol; 1,5-pentane diol; dipropylene glycol;2-methyl-1,5-pentane diol; 1,6-hexane diol; dimethanol decalin,dimethanol bicyclo octane; 1,4-cyclohexane dimethanol; triethyleneglycol; and 1,10-decane diol. In one embodiment, an alcohol may include3-ethyl-3-hydroxymethyl oxetane (commercially available as UVR6000 fromDow Chemicals (Midland, Mich.)).

Suitable bisphenols may include one or more dihydroxy-substitutedaromatic hydrocarbon. In one embodiment, a dihydroxy-substitutedaromatic compound may include one or more of 4,4′-(3,3,5-trimethylcyclohexylidene)-diphenol; 2,2-bis (4-hydroxyphenyl) propane (bisphenolA); 2,2-bis (4-hydroxyphenyl) methane (bisphenol F); 2,2-bis(4-hydroxyl-3,5-dimethylphenyl) propane; 2,4′-dihydroxy diphenylmethane;bis (2-hydroxyphenyl) methane; bis (4-hydroxyphenyl) methane; bis(4-hydroxyl-5-nitrophenyl) methane; bis(4-hydroxyl-2,6-dimethyl-3-methoxyphenyl) methane; 1,1-bis(4-hydroxyphenyl) ethane; 1,1-bis (4-hydroxyl-2-chlorophenyl ethane;2,2-bis (3-phenyl-4-hydroxyphenyl) propane; bis (4-hydroxyphenyl)cyclohexyl methane; 2,2-bis (4-hydroxyphenyl)-1-phenylpropane;2,2,2′,2′-tetrahydro-3,3,3′,3′-tetramethyl,1′-spirobi{1H-indene}-6,6′-diol (SBI); 2,2-bis(4-hydroxyl-3-methylphenyl) propane (DMBPC); and C1-C13alkyl-substituted resorcinols, and the like.

A suitable organic diluent may be added to an adhesive system accordingto embodiments of the invention. The organic diluent may decrease aviscosity of the adhesive system. Suitable reactive diluents mayinclude, but are not limited to, dodecylglycidyl ether,4-vinyl-1-cyclohexane diepoxide, and di (beta-(3,4-epoxy cyclohexyl)ethyl) tetramethyl disiloxane, or combinations of two or more thereof.Other diluents may include monofunctional epoxies and/or compoundscontaining at least one epoxy functionality. Such diluents may include,but are not limited to, alkyl derivatives of phenol glycidyl ethers suchas 3-(2-nonylphenyloxy)-1,2-epoxy propane or 3-(4-nonylphenyloxy)1,2-epoxy propane; glycidyl ethers of phenol; substituted phenols suchas 2-methylphenol, 4-methyl phenol, 3-methylphenol, 2-butylphenol,4-butylphenol, 3-octylphenol, 4-octylphenol, 4-t-butylphenol,4phenylphenol, and 4-(phenyl isopropylidene) phenol; and the like. Inone embodiment, the reactive diluent may include3-ethyl-3-hydroxymethyl-oxetane, which is commercially available asUVR6000 from Dow Chemical (Midland, Mich.).

A suitable flame retardant may include one or more material thatcontains phosphorus, iron, halogen, oxide, or hydroxide. In oneembodiment, a flame retardant additive may include phosphoramide,triphenyl phosphate (TPP), resorcinol diphosphate (RDP), bisphenol Adisphosphate (BPA-DP), organic phosphine oxide, halogenated resin (e.g.,tetrabromobisphenol A), metal oxide (e.g. bismuth oxide), metalhydroxide (e.g., MgOH), and combinations of two or more thereof.Suitable pigment may include one or both of reactive and non-reactivematerials.

In one embodiment, a cure system may be produced by dispersion of:refractory solids (e.g. CS) into a liquid curing agent and a solvent toform a solution. A suitable solvent may include a hydroxyl-group freesolvent, such as propylene glycol methyl ether acetate, toluene, xylene,supercritical fluid (e.g., SCF CO₂), and the like.

After the dispersion or mixing, the solvent may be removed. Suitablesolvent removal methods may include affecting the temperature and/orpressure to volatilize the solvent. That is, heat, vacuum, or both maybe used to extract or remove the solvent from the dispersion. If asupercritical fluid, such as supercritical carbon dioxide, is used, roomtemperature and pressure may be sufficient to remove the solvent.Subsequently, a solvent-free filled low temperature liquid cure systemaccording to an embodiment of the invention may be recovered and stored.

In one embodiment, a cure system further may be mixed with a curableresin to form an adhesive system. The resulting adhesive system may havea flowable or workable viscosity for a predetermined time, i.e., potlife. For a no-flow underfill application, the viscosity may be such toallow flow of the underfill during dispensing on the substrate andformation of solder electrical connection during a reflow process.Viscosity selection may be made by one or more of determining amounts ofrefractory solids in the resin, amounts of refractory solids in the curesystem, the initial unfilled viscosity of the resin and/or cure system,temperature, the presence or amount of additives or flow-modifiers,control over working pressure, use of sonic vibrations, and the like.

The adhesive system according to embodiments of the invention may beused in an electronic device. In one embodiment, the adhesive system maybe used as an underfill material, such as a no-flow underfill, in a flipchip assembly to secure a chip to a substrate. The adhesive system mayexhibit one or more of: prolonged room temperature stability, desirablesolder ball fluxing, and a coefficient of thermal expansion below about50 ppm/° C. when cured and used as, for example, an encapsulant or anunderfill. In one embodiment, a cured adhesive system may haveproperties that include one or more of a low CTE (below about 40 ppm/°C.), self-fluxing properties during application, a high Tg (above about100 degrees Celsius), a high heat deflection temperature (HDT), andrelatively high optical transparency.

An embodiment of the invention may provide a no-flow underfill materialhaving a coefficient of thermal expansion, when cured, of less than 50ppm/° C., in a range of from about 50 ppm/° C. to about 40 ppm/° C.,from about 40 ppm/° C. to about 30 ppm/° C., or less than about 30 ppm/°C. An embodiment may enable a final filler loading of greater than 30weight percent, a range of from about 30 weight percent to about 40weight percent, from about 40 weight percent to about 50 weight percent,or greater than about 50 weight percent, while maintaining one or moreof an acceptable level of processability, transparency, or a desirablyhigh glass transition temperature (Tg). Processability relates toproperties that may include flowability, viscosity, visco-elasticity,tack, wetability, out-gassing, percent void, shelf life, cure time, curetemperature, and the like. Transparency relates to the property ofpermitting the relatively free passage of electromagnetic radiationthrough a pre-determined thickness of material without one or morerefraction, reflection or absorption. Glass transition temperaturerelates to an inflection point on a plot of modulus versus temperature.The Tg indicates a temperature range above which a material may undergoplastic deformation, or may change from a rigid or brittle state to arubbery or softened state.

In one embodiment, an adhesive system may be a no-flow underfill, acapillary flow underfill, a wafer level underfill, a thermal interfacematerial (TIM), and/or pre-applied and optionally B-staged on asubstrate, and may be dispensable and have utility in the fabrication ofan electronic device, such as a computer, an optical device, or asemiconductor assembly. As an underfill material or encapsulant, theadhesive system may reinforce physical, mechanical, and electricalproperties of solder bumps that may secure a chip to a substrate, and/ormay act as flux during solder bump melting.

No-flow underfilling may include dispensing an underfill encapsulantmaterial on the substrate or semiconductor device and performing solderbump reflowing simultaneously with underfill encapsulant curing. Waferlevel underfilling may include dispensing underfill materials onto thewafer before dicing into individual chips that are subsequently mountedin the final structure via flip-chip type-operations. Alternatively tono-flow underfill, dispensing the underfill material may includeapplying in a fillet or bead extending along at least one edge of achip, and allowing the underfill material to flow by capillary actionunder the chip to fill all, or nearly all, gaps between the chip and thesubstrate.

In one embodiment, an adhesive according to embodiments of the inventionmay be energy cured, such as by heat, UV light, microwave energy,electron been energy, and the like. For heat or thermal curing, asuitable temperature may be in a range of from about 50 degrees Celsiusto about 100 degrees Celsius, from about 100 degrees Celsius to about200 degrees Celsius, from about 200 degrees Celsius to about 250 degreesCelsius, or greater than about 250 degrees Celsius. For no flowunderfill, the cure temperature is in a range of from about 183 degreesCelsius (melting point of eutectic solder) to about 230 degrees Celsiusfor Sn/Pb eutectic solder and from about 230 degrees Celsius to about260 degrees Celsius for lead-free solder. Curing may occur over a periodof less than about 30 seconds, in a range between about 30 seconds andabout 1 minute, from about 1 minute to about 5 minutes, from about 5minutes to about 30 minutes, from about 30 minutes to about 1 hour, fromabout 1 hour to about 5 hours, or greater than about 5 hours. For noflow underfill a cure process (during a reflow) may be in a range offrom about 3 minutes to about 10 minutes.

Optional post-curing may be performed at a temperature of less than 100degrees Celsius, in a range of from about 100 degrees Celsius to about150 degrees Celsius, or greater than about 150 degrees Celsius, over aperiod of less than one hour, in a range of from about 1 hour to about 4hours, or greater than about 4 hours. For no-flow underfill, the postcure may be at a temperature in a range of from about 100 degreesCelsius to about 160 degrees Celsius over a period of from about 1 toabout 4 hours. Other times, temperatures and pressures for curing andpost-curing may be selected with reference to application specificparameters.

In one embodiment, a cure system according to an embodiment of theinvention may consist essentially of a liquid curing agent andcompatiblized and passivated silica. In another embodiment, a curesystem may consist essentially of a liquid carboxylic acid anhydridecuring agent, and compatiblized colloidal silica treated with a cappingagent. In yet another embodiment, a cure system may consist essentiallyof a room temperature liquid anhydride-curing agent, and compatiblizedand passivated colloidal silica having a nano-size average particlediameter.

EXAMPLES

The following examples are intended only to illustrate methods andembodiments in accordance with the invention, and as such should not beconstrued as imposing limitations upon the claims. Unless specifiedotherwise, all ingredients are commercially available from such commonchemical suppliers as Alpha Aesar, Inc. (Ward Hill, Mass.),Sigma-Aldrich Corp. (St. Louis, Mo.), and the like.

Example 1 Preparation of Compatiblized and Passivated Solids

A mixture is made by adding 300 grams of SNOWTEX-ZL (80 nm averageparticle size) to 300 grams of isopropyl alcohol (IPA). After thoroughlymixing, 2 grams of phenyl trimethoxysilane (Ph(OMe)₃Si) is added to themixture. The resulting mixture is refluxed for three hours. Afterreflux, the mixture is cooled to room temperature. The cooled mixturehas 600 grams of methoxypropanol added while mixing, until thoroughlymixed. A stripping process removes 600 grams of volatile material, byweight. Hexamethyl disilazane (HMDZ) is added to the stripped mixture inan amount of 6 grams. The mixture is thoroughly mixed, refluxed for 1hour at elevated temperature, and then stripped to 200 grams totalweight. 300 grams of propylene glycol methyl ether acetate or1-methoxy-2-acetoxypropane (PGMEA) is added and mixed thoroughly. Theresulting mixture is stripped of 300 grams of volatile weight andfiltered. The yield is 250 grams of compatiblized and passivatedcolloidal silica material having solids of 29.10 weight percent. Therecovered sample is labeled Sample 1A. An ingredient list is shown inTable 1, below. The above disclosed process is repeated to form Sample1B, the difference being that silica having an average particle size of50 nm, rather than 80 nm, is used.

TABLE 1 Ingredient list for compatiblized and passivated solids (Sample1A) INGREDIENT AMOUNT (g) Snowtex-ZL 300 Snowtex-ZL 80 nm particles,Conc. OH = 5/nm² IPA 300 Ph(OMe)₃Si  2 Methoxypropanol 600 HMDZ  6 PGMEA300 Yield 215 Solids     29.10% Appearance white liquid

Example 2 through Example 4 Preparation of Cure System IncludingCompatiblized and Passivated Solids

The compatiblized and passivated colloidal silica materials produced inExample 1 (Samples 1A and 1B) are added to liquid anhydride materialsmethylhexahydrophthalic anhydride (MHHPA) and5,5′-(1,1,3,3,5,-hexamethyl-1,5-trisiloxane diyl) bis[hexahydro-4,7-methanoisobenzofuran-1,3-dione] (TriSNBA) to form Samples2-4. Samples 2-4 were evaporated using a commercially available rotaryevaporator at 70 degrees Celsius. Rotary evaporators may be obtainedfrom, for example, Thomas Industries, Inc. (Skokie, Ill.). An ingredientlist for the cure systems containing compatiblized and passivated silicais shown in Table 2. A list of properties for the Samples 2-4 shown inTable 2 is shown is Table 3. The viscosity measurements are performedwith SP # 40 at 10 rpm, and the results are in centipoise, unlessotherwise indicated.

TABLE 2 Ingredient list for cure systems containing Samples 1A and 1B).Sample 2 Sample 3 Sample 4 Sample 1A 35 35 — (80 nm ave size) Sample 1B— — 37.3 (50 nm ave size) MHHPA 10 — 10 TrisNBA/MHHPA — 10 — (40/60ratio)

TABLE 3 Properties for cure systems (Samples 2-3) that contain Samples1A and 1B. Sample 2 Sample 3 Sample 4 Appearance yellow yellow lightyellow Mass 20.15 20.06 20.1 % solids 50 50 50 Viscosity (centipoise)600 3040 920

Example 5 and Example 6 Preparation of Adhesive Systems that Include aCure System

An aliphatic dioxirane monomer, CYRACURE UVR 6105 is blended withBisphenol F epoxy resin in a 75/25 ratio to form a base resin. Areactive diluent, UVR6000, is added to the base resin to form a mixture.A cure catalyst, POLYCAT SA-1, is added to the mixture of base resin anddiluent to form a catalyzed mixture. The catalyzed mixture is blendedwith 60 weight percent of a cure system (Samples 2 or 3) at roomtemperature for approximately 10 minutes to form an adhesive system(Samples 5 and 6, respectively). After which, each adhesive system(Samples 5 and 6) is degassed at relatively high vacuum at roomtemperature for 20 minutes. Samples 5 and 6 are stored at negative 40degrees Celsius.

For test and evaluation, Samples 5 and 6 are applied to a chip and to asubstrate. The chip and substrate are set together to form an assembly.Thermal energy is applied to cure the adhesive systems, Samples 5 and 6.Test results are listed in Table 5. Viscosity is performed with spindle#40 at 20 rpm at room temperature, the results are in centipoise.

TABLE 4 Ingredient list for adhesive systems (Sample 5 and Sample 6)that each include a curable resin and a cure system. INGREDIENT Sample 5Sample 6 Base Resin 1 5 5 Sample 2 4.07 — Sample 3 — 5 UV R6000 0.2 0.2Polycat SA-1 0.0188 0.0216

TABLE 5 Properties list for adhesive systems. Test Sample 5 Sample 6Fluxing of eutectic solder Good Good Viscosity (centipoise) 4880 29700   % solids 53% 52% Tg TMA (° C.) 138.0 154.0 CTE-20-80 (ppm/° C.) 36.0  39.0 DSC peak (° C.) 214.4 208.1 DSC H onset (° C.) 164.4 154.7DSC H (J/g) 199.0 168.8 DSC Tg (° C.) 123.5 147.0

The foregoing examples are merely illustrative, serving to illustrateonly some of the features of the invention. The appended claims areintended to claim the invention as broadly as it has been conceived andthe examples herein presented are illustrative of selected embodimentsfrom a manifold of all possible embodiments. Accordingly it isApplicants' intention that the appended claims are not to be limited bythe choice of examples utilized to illustrate features of the presentinvention. As used in the claims, the word “comprises” and itsgrammatical variants logically also subtend and include phrases ofvarying and differing extent such as for example, but not limitedthereto, “consisting essentially of” and “consisting of.” Wherenecessary, ranges have been supplied, those ranges are inclusive of allsub-ranges there between. It is to be expected that variations in theseranges will suggest themselves to a practitioner having ordinary skillin the art and where not already dedicated to the public, thosevariations should where possible be construed to be covered by theappended claims. It is also anticipated that advances in science andtechnology will make equivalents and substitutions possible that are notnow contemplated by reason of the imprecision of language and thesevariations should also be construed where possible to be covered by theappended claims.

1. A cure system, comprising: a curing agent that is a low temperatureliquid; and a finely divided refractory solid, wherein the solid has anactive termination site density that is less than about 5 per squarenanometer and, wherein the solid is non-reactive relative to the curingagent.
 2. The cure system as defined in claim 1, wherein the solid iscompatibilized and passivated.
 3. The cure system as defined in claim 2,wherein the curing agent comprises an anhydride.
 4. The cure system asdefined in claim 3, wherein the anhydride comprises one or more aromaticcarboxylic acid anhydride, aliphatic carboxylic acid anhydride,cycloaliphatic carboxylic acid anhydride, or siloxane dianhydride. 5.The cure system as defined in claim 3, wherein the anhydride comprisesone or more of benzoic anhydride; phthalic anhydride; hexahydro phthalicanhydride; methyl-hexahydro phthalic anhydride (MHHPA); 4-nitrophthalicanhydride; naphthalene tetracarboxylic acid dianhydride; naphthalicanhydride; tetrahydro phthalic anhydride; cyclohexane dicarboxylicanhydride; butanoic anhydride; dodecenyl succinic anhydride;2,2-dimethyl glutaric anhydride; ethanoic anhydride; glutaric anhydride;hexafluoro glutaric acid anhydride; itaconic anhydride;tetrapropenylsuccinic anhydride; maleic anhydride; 2-methyl glutaricanhydride; 2-methyl propionic anhydride 1,2-cyclohexane dicarboxylicanhydride; octadecyl succinic anhydride; 2-octenyl succinic anhydride;n-octenyl succinic anhydride; 2-phenylglutaric anhydride; propionic acidanhydride; 3,3-tetramethylene glutaric anhydride; or derivativesthereof.
 6. The cure system as defined in claim 1, wherein the curingagent is a liquid at a temperature in a range of less that about 100degrees Celsius.
 7. The cure system as defined in claim 6, wherein thecuring agent is a liquid at a temperature in a range of less that about50 degrees Celsius.
 8. The cure system as defined in claim 7, whereinthe curing agent is a liquid at a temperature in a range of from about25 degrees Celsius to about 35 degrees Celsius.
 9. The cure system asdefined in claim 1, wherein the refractory solid comprises silica. 10.The cure system as defined in claim 9, wherein the silica comprisessilica particles.
 11. The cure system as defined in claim 10, whereinthe silica particles have an average particle size that is nano-scale.12. The cure system as defined in claim 11, wherein the silica particleshave an average particle size in a range of less than about 100nanometers.
 13. The cure system as defined in claim 1, furthercomprising a catalyst or an accelerator.
 14. The cure system as definedin claim 1, further comprising one or more of pigment, reactive diluent,defoamer, flow modifier, flexibilizer, or flame retardant.
 15. The curesystem as defined in claim 1, further comprising an adhesion promoter.16. The cure system as defined in claim 1, wherein the solid comprisesone or both of alumina or boron nitride.
 17. The cure system as definedin claim 1, wherein the solid is present in an amount in a range ofgreater than about 30 weight percent based on the total weight of thecomposition.
 18. The cure system as defined in claim 17, wherein thesolid is present in an amount in a range of from about 30 weight percentto about 70 weight percent based on the total weight of the composition.19. An adhesive system comprising the cure system as defined in claim 1,and further comprising a curable resin.
 20. The adhesive system asdefined in claim 19, wherein the curable resin comprises one or moreepoxy or oxirane moiety.
 21. The adhesive system as defined in claim 20,wherein the epoxy comprises one or more aliphatic epoxy resin,cycloaliphatic epoxy resin, or aromatic epoxy resin.
 22. The adhesivesystem as defined in claim 19, wherein the curable resin is presentrelative the cure system in a stoichiometric ratio in a range of about1:1.
 23. The adhesive system as defined in claim 19, wherein the curableresin comprises a filler prior to mixing with the cure system.
 24. Acured polymer layer comprising the adhesive system as defined in claim19.
 25. An electronic device, comprising: a substrate; a chip secured tothe substrate; and a cured polymer layer as defined in claim 24 disposedbetween the chip and the substrate.
 26. A solvent-free adhesive systemfor use in an electronic device, comprising: a curable resin comprisinga first portion of refractory solid; and a cure system operable to curethe resin, the cure system comprising a curing agent and a secondportion of refractory solid, wherein the refractory solid is present inan amount greater than about 30 percent by weight relative to the totalweight of the adhesive system and wherein the first and second portionof refractory solids each have an active termination site density thatis less than about 5 per square nanometer.
 27. The adhesive system asdefined in claim 26, wherein a mixture of the resin and the curing agenthas a viscosity at about room temperature that is sufficiently low toenable application of the mixture to a substrate surface and to use as ano-flow underfill.